1. Field of the Invention
The present invention relates to a hologram recording and reproducing apparatus that records and reproduces a hologram, and to a method of recording and reproducing the hologram.
2. Description of the Related Art
Hologram recording and reproducing apparatuses so far developed include one disclosed in JP-A-2002-216359. The hologram recording and reproducing apparatus disclosed therein basically works as follows. The hologram recording and reproducing apparatus splits a laser beam emitted by a laser light source into an information beam and a reference beam, and modulates the information beam with a spatial light modulator to illuminate a discal recording medium (disk), while transmitting the reference beam to the disk to form an illumination spot thereon, such that the illumination spot is superposed on the information beam on the disk. As a result, the information beam and the reference beam interfere with each other on a unit sector on the disk corresponding to the illumination spot, thus creating a hologram is recorded on the disk in a form of an interference fringe pattern. When the disk was rotated at a certain angular increment, the illumination spot was relatively moved. Forming an illumination spot each time the disk is stopped leads to formation of a multitude of unit sectors circumferentially aligned on the disk at a constant pitch to constitute a track.
For reading out the hologram in a reconstruction process, the illumination spot only containing the reference beam is positioned on the track including a desired unit sector, and the disk is rotated in one direction by the increment corresponding to the pitch of the unit sectors, as in a seek action of a popular photomagnetic disk apparatus. Thus, the illumination spot only containing the reference beam is positioned on each unit sector to receive a reconstruction beam emitted by each unit sector, whereby the desired hologram is reconstructed. For sequentially reproducing the hologram from a plurality of unit sectors, the foregoing action is repeatedly performed.
In the conventional hologram recording and reproducing apparatus as described above, however, the disk is stopped so as to illuminate a unit sector in the reconstruction process at every time determination is required whether the hologram contains the desired information. In this operation, the recording medium is always rotated in one predetermined direction. As a result, a standby time corresponding to one entire rotation at maximum can be spent in addition to the seek time in the process to move the illumination spot relatively from the current unit sector to the unit sector from which the hologram is to be reconstructed. Accordingly, the conventional hologram recording and reproducing apparatus requires a considerably longer access time than other popular photomagnetic disk apparatuses, and hence has a room for improvement in the aspect of the access time.